Composition Analysis Uncertainty: Impact, Common Causes and Use of
Keith Trischan, Michael Ruschak, Jay Goodman, Becky Wyss, Mike Brandt,
Production Limit Offsets to Ensure On-Composition Product
Alcoa Technical Center, Alcoa Center, Pennsylvania, USA
Track: BILLET PROCESS & EQUIPMENT - Alloys
ABSTRACT—Every pound of aluminum alloy produced and sold is guaranteed to meet the Aluminum
Association Inc. registered limits, or other specified composition limits for the alloy. Variability present
in the analysis process used to certify the composition is often overlooked when determining compliance
with composition limits. This can result in a broad range of consequences from the relatively benign, such
as inconsequential shifts in mechanical properties, to potential safety or product liability issues leading to
product recall and subsequent legal action. This presentation discusses the potential impact of analysis
variability, root causes of intra- and inter-location variability, and approaches which ensure production of
metal that is within composition specifications through the use of offsets.
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